This invention relates to a method for creating high aspect ratio structures in perovskite materials, including high-temperature superconductors using ion irradiation to modify bulk superconducting material.
There has been a rapid growth in the number of applications based on Micro-electromechanical Systems (MEMS). In 1997, the MEMS market exceeded U.S. $2 B, and the growth curve is exponential resembling that of the semiconductor industry. The most common applications include pressure and inertial sensing (automotive air bags, gyroscopes) while immediate growth potential is in xe2x80x9clight handlingxe2x80x9d applications (fiber-optic interconnects and switches). This relatively fast transition from RandD to commercial applications is due to the fact that the current MEMS technology is based on Si and is therefore 100% compatible with the semiconductor manufacturing process. Although providing a short-term advantage in the commercial acceptance of MEMS technology, the limitation of the Si materials significantly restricts the diversity of MEMS applications.
The most serious materials limitation in MEMS technology is in producing and controlling motion. The choice of Si and GaAs confines the available actuation mechanisms to electrostatic and thermal. These microactuation methods are either weak (electrostatic) or highly dissipative and slow (thermal). Magnetic actuation using superconductors is expected to provide a significant increase in energy density, a faster response time, and very low dissipation.
Irradiation with ions is a well-known technique that has been extensively used in nuclear physics and materials science. In material science the effect of exposure to ion irradiation has mostly been used to study the target material properties. Any applications of ion irradiation are mainly derived from damages and/or modification inflicted on materials by the impinging ions.
When energetic ions hit the target material they create tracks (defects) inside the target. The microscopic modification of the material is concentrated along the paths traversed by the impinging ions through the material. While passing through the target material the ions lose kinetic energy due to electronic and nuclear scattering with the target molecules. Depending on the combination of target material, the ion beam type, and the kinetic energy of the projectile ions different types of defects can be produced in the target material. The radiation effectively modifies the target material structure and with it the local chemical and physical properties of the irradiated material, that is the tracks or defects. For example, it is well known that ion irradiation in high temperature superconductors increases the critical current.
We have discovered a novel method to modify and process high temperature superconductors (HTSC) on a microscopic level that allows effective integration of superconducting materials into a variety of structures such as MEMS and the invention also includes the structures themselves. This discovery creates an opportunity to exploit the unique properties of superconductors and to design a qualitatively new class of superconducting smart microstructures that can exert extremely high magnetic actuation force densities with virtually no dissipation. These high actuation force densities provide the long-needed mechanism for transmitting mechanical power from the microscopic world of MEMS to the macroscopic world of traditional technology. This invention integrates basic materials science, creative materials modification, and novel device fabrication to dramatically expand the horizon for MEMS technology, with respect to high temperature superconductors, such as yttrium-based systems, bismuth based systems and thallium based systems.
This invention relates to a method for fabricating high aspect ratio structures, as well as the structures themselves, in perovskite and other materials having important properties useful in superconducting, optical, electronic, electrochemical, and other systems. Thicker structures in these systems allows the use of larger forces and/or power levels in devices such as optical switches, miniature pumps, RF and microwave receivers and transmitters, and other products. Fabrication techniques for thinner structures, such as structures having thicknesses in the range of from about 0.1-5 xcexcm, 0.1 xcexcm to about 5 xcexcm have been difficult to apply in the fabrication of thicker structures, such as those having thicknesses greater than about 10 xcexcm, and the problems have led to the development of this invention. It is understood that the invention may be the first of a more promising method to produce thicker structures with the required precision and certain other characteristics.
More particularly, the invention relates to new structures and a method for fabricating new structures having a thickness in the order of 10-20 microns and above from a variety of superconducting materials through a multiple step operation. With a perovskite material useful as a high temperature superconductor as an example, the invention involves the steps of applying controlled spatial ion irradiation in a predetermined pattern to form an etchable surface and underlying material and a non-etchable surface and underlying material. Subsequently, a chemical or other etchant, such as EDTA (ethylene diamine tetracetic acid) or KOH or NaOH or Br in methanol ethanol is used to remove the irradiated material to leave the desired structure. The shape of the structure is achieved with a high precision on the order of 0.1 xcexcm.
The ion irradiation is effective at to depths of at least 10 microns and up to about 100 microns, depending on the energy of the ion beam and the particular ions used. Heavy ions, such as Pb, Au and U are preferred. Chemical etchants include KOH, NaOH and EDTA as well as mineral acids, such as Br in alcohol. As described briefly above, the thicker structures provided by this invention will allow the application or generation of larger forces and/or power levels to a variety of structures or devices such as optical switches, pumps, RF transmitters, and the like, in optical, micromechanical, and other systems.
Our newly discovered process of controlled nano-size structural and chemical bulk modification of HTSC (YBCO is used by way of example only) provides a lithographic process for forming very high tolerance high aspect ratio superconducting microstructures. By high aspect ratio, we mean a structure having a generally flat surface, a ratio of the thickness of the depth or thickness of the structure to the smaller lateral dimension of the structure of not less than 2:1 and preferably greater than 3:1. A side wall substantially perpendicular to the flat surface is needed. In addition, the invention produces precisely controlled introduction of strong pinning centers inside the HTSC material. As a result, smart superconducting microstructures can be produced with very well defined spatial and electromagnetic characteristics. Their use in MEMS as well as in other areas opens a new class of actuation devices that feature very high actuation forces with very small losses.
Commercial applications are in three basic areas: actuation, sensing and superconducting passive electronic components. Actuation devices include superconducting micromachines such as micromotors, micropumps, and drives that exploit the high energy density offered by HTSC materials. Sensing applications include airborne telemetry and tunable IR devices based on HTSC bolometers and SQUIDS. Passive electronics components for wireless communication such as tunable high power RF and microwave filters/resonators will have significantly higher power handling capability due to the 3D bulk character and high aspect ratio of the devices produced by our method. The technology also applies to flight and space applications of microactuators due to the large ratio of useful work to device weight.
Accordingly, it is an object of the present invention to provide a method of fabricating high aspect ratio ceramic structures, comprising providing a perovskite or perovskite-like crystalline material; exposing a selected portion of the crystalline material to a high energy ion beam for a time sufficient to cause the crystalline material contacted by the ion beam to have substantially parallel columnar defects, and thereafter etching selected portions of the material having substantially parallel columnar defects leaving material with and without substantially parallel columnar defectors in a predetermined shape having high aspect ratios of not less than 2 to 1.
Yet another object of the invention is to provide a structure a structure of a ceramic which is superconducting at a temperature in the range of from about 10xc2x0 K. to about 90xc2x0 K. having substantially parallel columnar defects in which the smallest lateral dimension of the structure is less than about 5 microns, and the thickness of the structure is greater than 2 times the smallest lateral dimension of the structure.
Still another object of the present invention is to provide A structure made by the method of fabricating high aspect ratio ceramic structures, comprising providing a perovskite or perovskite-like crystalline material; exposing a selected portion of the crystalline material to a high energy ion beam for a time sufficient to cause the crystalline material contacted by the ion beam to have substantially parallel columnar defects, and thereafter removing selected portions of the material having substantially parallel columnar defect areas leaving material with substantially parallel columnar defects in a predetermined shape having high aspect ratios of not less than 2 to 1.
A final object of the present invention is to provide a method of fabricating high aspect ratio ceramic structures, comprising providing a high temperature superconducting perovskite or perovskite-like crystalline material; masking some of the material with a substance capable of shielding the material from a high energy ion beam, exposing the unshielded portion of the crystalline material to a high energy ion beam for a time sufficient to cause the crystalline material contacted by the ion beam to have substantially parallel columnar defects to form a first geometrical shape of the high temperature superconducting material with improved pinning characteristics, thereafter etching selected portions of the material having substantially parallel columnar defects by e-beam or optical lithography leaving material with and without substantially parallel columnar defectors in a second predetermined shape having high aspect ratios of not less than 2 to 1.